1. Field of the Invention
The following description relates to the use of light emitting diodes (LEDs) in lighting applications, and, more specifically, to the use of LEDs to illuminate outdoor and public environments with light fixtures having a decorative and pleasant appearance.
2. Description of the Related Art
In certain outdoor and public environments, especially those environments in which lack of lighting is an issue, it is necessary to provide illumination for public safety and liability purposes. While the need for this illumination is geared primarily toward public safety and proactive preventative measures, it is generally desired that the provided illumination be implemented in an attractive and pleasing manner that will enhance the decorative ambiance of the particular environment.
Luminaires are conventionally implemented in these types of environments. Luminaires are light fixtures that can be designed to provide an optimal amount of illumination in an attractive manner that is pleasing to the eye. Luminaires can be designed in many different shapes and sizes to provide attractive illumination specific to the needs of the particular environment.
The conventional and long-standing light source that is used within a luminaire to output light is a high pressure sodium (HPS) device. The HPS device is largely similar in effect to a conventional incandescent light bulb used residentially in home lighting applications. Like such a bulb, the HPS device emits light in a 360 degree pattern providing uniformity of illumination throughout the luminaire.
However, there are a number of drawbacks to using HPS devices in luminaires. The HPS device is a high energy device that requires 120 V AC to operate. The HPS device converts the 120 V AC to a higher voltage at the luminaire. Then, the higher voltage at the luminaire increases until it spikes, creating a “strike arc”. This creates unsafe high currents which could prove deadly to human and animal life in certain situations. In addition, the HPS device generally requires more energy as it draws nearer to the end of its life span.
Moreover, the HPS device creates light by burning gas. In turn, the burning of the gas creates a tremendous amount of heat. Again, the amount of heat created by the HPS device could be hazardous to both humans and animals. The HPS device also contains mercury, which is known to be hazardous to humans and animals as well as the environment.
Further, the HPS device has a high maintenance requirement. Specifically, the HPS device utilizes a ballast. This ballast has a typical life in a range of 3-5 years. Also, the HPS device utilizes a bulb having a typical life span in a range of 10,000 to 24,000 hours. The life span of the bulb may be further negatively affected by various shock and vibration.
In addition, the HPS device has very poor color rendering and produces an extremely yellow light, which, in turn, affects the color of objects being illuminated by the HPS device. For example, a car having a brown color in normal lighting may have a black color when illuminated by the HPS device. Also, a sweatshirt having a red color in normal lighting may have a dark brown color when illuminated by the HPS device. Moreover, the human eye has a decreased sensitivity to yellow light, which further exacerbates the color rendering problems of the HPS device.
The HPS device is also extremely slow to illuminate, typically requiring five minutes to arrive at full illumination levels. Moreover, when the HPS device loses power for even a fraction of a second, the HPS device is required to go through a cool-down/restart period. This cool-down/restart period requires up to seven minutes for the HPS device to resume full illumination levels after any short loss of power.
Needless to say, an alternative to using the HPS device with luminaires has been long-sought after. Metal halide devices have replaced the HPS devices in some situations. However, while producing better color rendering than HPS devices, metal halide devices have shorter lives than HPS devices. Metal halide devices also are not nearly as efficient as HPS devices. Thus, metal halide devices can only be used in certain applications.
In summary, an alternative to the use of HPS devices in luminaires is still being sought. A light source is desired having a low energy requirement, a maintained voltage and current, low heat generation, low maintenance, shock and vibration resistance, a long life span, good color rendering, little delay in producing illumination, and no harmful elements.